The process of fermentation production of chemical products using sugars as raw materials has been used to produce various industrial materials. At present, as the sugars to be used as fermentation feedstocks, those derived from food materials such as sugar cane, starch, and sugar beet are industrially used. However, in view of the fact that increases in the price of food materials is expected due to future increases in the world population, or in an ethical view of the fact that those sugars compete with sugars for food, a process of efficiently producing a sugar liquid from a renewable nonfood resource, that is, cellulose-containing biomass, or a process of using an obtained sugar liquid as a fermentation feedstock to efficiently convert it to an industrial material, needs to be constructed in the future.
As a method of producing a sugar liquid from cellulose-containing biomass, a method of producing a sugar liquid by hydrolysis of cellulose-containing biomass using dilute sulfuric acid followed further by saccharification using an enzyme such as cellulase, as well as a method of producing a sugar liquid by hydrolysis of cellulose and hemicellulose with acid using concentrated sulfuric acid, is known (A. Aden et al., “Lignocellulosic Biomass to Ethanol Process Design and Economics Utilizing Co-Current Dilute Acid Prehydrolysis and Enzymatic Hydrolysis for Corn Stover,” NREL Technical report (2002)). A method of producing a sugar liquid by hydrolysis of cellulose-containing biomass with hot compressed water at 240 to 280° C. followed further by saccharification using a saccharifying enzyme is also disclosed (JP 3041380 B2). Among them, in recent years, methods of hydrolysis of biomass using a saccharifying enzyme, which methods use less energy and cause less environmental load but produce sugar at high yields, have been extensively studied. However, methods of producing a sugar liquid using a saccharifying enzyme result in high cost of production of a sugar liquid as the cost of the enzyme is high.
As a means of solving the above-mentioned technical problem in methods of producing a sugar liquid using a saccharifying enzyme, a method of recovering and reusing a saccharifying enzyme which has been used for hydrolysis has been proposed. For example, disclosed are a method in which an enzyme is recovered by filtering, through an ultrafiltration membrane, the sugar liquid obtained by continuous solid-liquid separation through a spin filter (JP 2006-87319 A), a method in which addition of a surfactant at the stage of saccharification of an enzyme suppresses adsorption of the enzyme and enhances the recovery efficiency of the enzyme (JP 63-87994 A) and the like. Also disclosed are a method in which hydrolysis of biomass using the recovered enzyme prior to the next and later saccharification reactions can enhance the recovery efficiency of the enzyme at the saccharification reactions and reduce the amount of enzyme used (WO 2011/115040) and other methods. In WO '040, the recovered enzyme in the Examples is the same filamentous fungus-derived enzyme as the enzyme used for the saccharification reaction, and Trichoderma is used in the Examples.
As above-mentioned, a method of recovering the enzyme used for hydrolysis of cellulose-containing biomass has been developed, but its effect is still insufficient in view of reduction of the amount of a saccharifying enzyme used, and a method of producing a sugar liquid with more effective usage of a saccharifying enzyme in producing a sugar liquid from cellulose-containing biomass is demanded.
Accordingly, it could be helpful to provide a method of producing a sugar liquid that can further enhance the effect of reduction in the amount of a saccharifying enzyme used.